Joe has finished his frist-aid course. He proves extremely helpful2/50Joe has finished his frist-aid course. He proves extremely helpful as a rescue worker.Although Joe proves extremely helpful as a rescue worker, he hasn’t finished his first-aid course.Without finishing his first-air course, Joe proves extremely helpful as a rescue worker.However helpful Joe proves as a rescue worker, he hasn’t finished his first-aid course.Having finished his first-aid course, Joe proves extremely helpful as a rescue worker.Giải thíchĐáp án D. Câu D là câu có 2 mệnh đề, trong đó mệnh đề phụ đã được rút gọn chủ ngữ.